Compressed natural gas (CNG) is a high octane fuel that is beneficial for reducing engine knock, for reducing hydrocarbon emissions in cold start events, and for reducing carbon dioxide emissions during engine operations. However, CNG has a low energy density compared to liquid hydrocarbon fuels, such as diesel fuel or gasoline. To increase the range and total fuel quantity stored in a vehicle, CNG may be utilized in conjunction with gasoline or diesel fuel, requiring the vehicle to switch between fuels for optimal performance. However, inclusion of separate fuel tanks may not be suitable in a vehicle due to space constraints. A preferable system may be one that stores liquid fuel and pressurized gaseous fuel together in single fuel tank. In particular, CNG is substantially soluble in gasoline or diesel fuel when stored together at a relatively low pressure (˜100 psi).
The inventors herein have recognized potential issues with the above approach. Namely, when a first fuel and a second fuel are stored together in the same fuel tank, each of the fuels may be partially soluble in the other fuel, and it is complicated to separately quantify the amount of each fuel remaining in the fuel tank. For example, the measured liquid fuel volume may comprise a first fuel and a portion of the second fuel solubilized in the first fuel. Furthermore the temperature, pressure and fuel composition in the fuel tank may change during engine operation and as portions of the first fuel and the second fuel are consumed. Accordingly, the amount of the second fuel solubilized in the first fuel may change during engine operation.
One approach which at least partially addresses the above issues includes a method, comprising on board a vehicle, measuring a volume of a liquid fuel in a fuel tank, wherein the liquid fuel comprises a first fuel and a second fuel, based on the volume of the liquid fuel, calculating a volume of a gaseous fuel in the fuel tank, wherein the gaseous fuel comprises essentially the second fuel, determining a solubility of the second fuel in the first fuel, and based on the solubility of the second fuel in the first fuel, determining a quantity of the first fuel in the fuel tank and a quantity of the second fuel in the fuel tank.
In another embodiment, a method of operating an engine may comprise, during a first condition, determining a solubility of the second fuel in the first fuel, determining a quantity of a first fuel and a quantity of a second fuel in the fuel tank based on the solubility of the second fuel in the first fuel, and adjusting a first fuel indicator and a second fuel indicator based on the quantity of the first fuel and the quantity of the second fuel in the fuel tank.
In another embodiment, a fuel system may comprise, a fuel tank on board a vehicle, the fuel tank comprising a liquid fuel and a gaseous fuel stored therein, a liquid fuel level sensor and a pressure sensor positioned at the fuel tank, and a controller, with executable instructions to, during a first condition, measure a volume of the liquid fuel in the fuel tank with the liquid fuel level sensor, wherein the liquid fuel comprises a first fuel and a second fuel, measure a pressure of the fuel tank with the pressure sensor, based on the volume of the liquid fuel, calculate a volume of the gaseous fuel in the fuel tank, wherein the gaseous fuel comprises essentially the second fuel, determine a solubility of the second fuel in the first fuel based on the pressure and temperature, and based on the solubility of the second fuel in the first fuel, determining a quantity of the first fuel and a quantity of the second fuel in the fuel tank.
In this way, a technical result may be achieved in that a quantity of the first fuel and a quantity of the second fuel may be accurately determined to provide an accurate indication of fuel remaining in the fuel tank to a vehicle operator. Furthermore, engine operation may be adjusted based on the quantity of the first fuel and the quantity of the second fuel to reduce engine emissions, reduce engine knock, and increase fuel economy. The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.